The present invention relates to a monoazo dye and, in particular, it relates to a blue monoazo dye with a novel crystal modification which is outstanding in its dispersion properties.
Furthermore the present invention also relates to a method in which this monoazo dye is used for the dyeing of fibre, especially polyester fibre and, in particular, it relates to a method for the dyeing of fibre, especially polyester fibre, under conditions which are more severe than hitherto.
In recent years, in the world of dyeing the methods of dyeing have been variously rationalized. For example, in the case of the dyeing of polyester fibre using disperse dyes, for fabric there are liquid flow dyeing methods and for yarn there are cheese dyeing methods or package dyeing methods, and the like, and these methods are widely carried out.
Since these dyeing methods comprise systems in which dyeing is performed by forcibly circulating a dye dispersion liquor through stationary close-packed layers in which a number of layers of fibre have been wound, it is particularly important that the dispersion properties of the dye in the dye bath be more outstanding than in the past. If, due to poor dispersion, dye particles aggregate together and produce comparatively large aggregates, a dye particle filtration phenomenon by the fibre layers occurs, and because of poor penetration of the dye into the fibre interior and adhesion of the aggregates at the surface of the item being dyed, etc, problems arise such as uneven depths of dyeing at the inner and outer layers, and a lowering of fastness such as rubbing fastness and the like.
In particular, very recently, from the point of view of economizing on resources and energy, there has been a move towards more severe dyeing conditions, namely (1) lowering the bath ratio of the dye bath (for example lowering the ratio of the material being dyed to the dye liquor from 1:30 to 1:10), (2) lowering tile proportion of the dispersing agent used (for example lowering the ratio of the dye cake to the dispersing agent from 1:3 to 1:1), (3) raising the temperature and shortening the time of dyeing (for example changing the dyeing conditions from 1 hour at 130xc2x0 C. to 0.5 hour at 135xc2x0 C.), and (4) increasing the rate and lowering the time of heating (for example from 1xc2x0 C./min to 2xc2x0 C./min), but such conditions all work to the disadvantage of the dye dispersion stability, so from this standpoint dyes with better dispersion properties are needed all the more.
Because of this situation, quite a number of the dyes which have been comparatively satisfactory in their dispersion properties hitherto have become inadequate in terms of their dispersion properties in the more demanding recent dyeing methods and dyeing conditions.
For Example, the acetanilide type monoazo dye represented by structural formula (I) 
which is obtained by performing a coupling reaction between a diazo component and a coupling component, uniformly dyes polyester fibre under the conventional mild dyeing conditions and is outstanding too in terms of the different measures of fastness, but under more severe conditions as described above its dispersion is inadequate and it is extremely difficult to obtain dyed materials of a uniform depth of dyeing.
Moreover this dye also has a problem in terms of its compatibility with various dyeing auxiliaries. For example, its high temperature dispersion stability in the presence of Glauber""s salt (Na2SO4) is extremely poor and, consequently, when the dyeing of polyester/cotton mixed-spun products is carried out jointly using a reactive dye or the like in the presence of Glauber""s salt, there is non-level dyeing. Furthermore, when used as a mixture with other dyes, there has been the problem that, because of poor compatibility with the mixed dye, colour variation and uneven dyeing arise.
Consequently, there is an increasingly greater need for dyes which are outstanding in their dispersion properties and which, even when employing more severe dyeing methods and conditions, produce level dyeing with outstanding fastness.
Thus, the problem addressed by the present invention is to resolve the aforesaid conventional difficulties and to provide a dye which is excellent in its dispersion properties.
As a result of a painstaking investigation of the above difficulties, the present inventors have discovered: that there are present in the acetanilide type monoazo compound represented by structural formula (I) at least two types of crystal modification, one of these being the crystal modification obtained by the normal conventional method and the other being a novel crystal modification; and that the stability of the dispersed state in the dyestuff dye bath is strongly related not just to the size of the dye particles but also to the crystal modification present; and that when the compound displays the aforesaid novel crystal modification it is markedly more outstanding in its dispersion properties than the conventional crystal modification; and also that by using this compound as a dye it is possible to obtain a dye which gives more satisfactory dyeing under both conventional dyeing conditions and more severe conditions. It is based on these discoveries that they have arrived at the present invention.
Thus, the present invention provides a water-insoluble monoazo dye represented by the structural formula (I), of a crystal modification characterized by an X-ray diffraction pattern (CuKxcex1) showing one strong peak at a diffraction angle (2xcex8) of 11.1xc2x10.1xc2x0 and also four intermediate peaks at 8.1xc2x10.1xc2x0, 21.8xc2x10.1xc2x0, 23.1xc2x10.1xc2x0 and 25.2xc2x10.1xc2x0.
The novel crystal modification of the present invention (hereinafter referred to as the (xcex1-form crystal modification) can be obtained in the following manner.
For example, the monoazo compound of aforesaid structural formula [I] is synthesized by diazotizing 6-chloro-2,4-dinitroaniline in the usual way, and then carrying out a coupling reaction with the coupler 3-(N,N-diallyl)amino-4-methoxyacetanilide in an aqueous medium at a temperature of 5 to 15xc2x0 C., and preferably 0 to 10xc2x0 C., for from 0.5 to 15 hours.
Taking the crystal modification in the cake of the monoazo compound obtained by such synthesis as the xcex2-form crystal modification, in the present invention this cake is converted to the xcex1-form crystal modification by further treatment under specified conditions. The treatment method employed comprises for example, (1) the method of dispersing the cake of the xcex2-form crystal modification in an aqueous medium, in certain circumstances in the presence of a dispersing agent such as a formaldehyde condensate of naphthalene sulphonic acid, or a concentrate of sulphide pulp waste liquor in which the chief component is sodium lignin sulphonate, and then carrying out a stirring treatment at a temperature of 60 to 130xc2x0 C., preferably 80 to 100xc2x0 C., for 0.5 to 30 hours, preferably from 1 to 10 hours, and (2) the method of dispersing the cake of the xcex2-form crystal modification in an organic solvent such as an alcohol like methanol, ethanol or butanol, an ether such as dioxane, or ethylene glycol or glycol ether, and carrying out a stirring treatment at a temperature of 15 to 100xc2x0 C., preferably 20 to 80xc2x0 C., for 0.5 to 10 hours.
Next, the xcex1-form crystal modification and the xcex2-form crystal modification of the monoazo compound represented by aforesaid structural formula [I] are explained by means of the drawings.